An AC generator generates power by using the driving force transmitted from an engine, charges a battery, and supplies power to various kinds of electronic parts. Reducing the size, the weight and the cost of the AC generator while improving the output power is a critical issue to maintain or improve the competitiveness in the market.
A method for manufacturing a rectifying device for an AC generator is proposed in U.S. Pat. Document No. U.S. Pat. No. 5,828,564 (JP-A-10-242671). In this method, a rectifying element is press-fitted in a through hole formed in a radiation plate. The rectifying element is fixed and electrically connected to the radiation plate with a simple process. As a result, the manufacturing cost is reduced.
Furthermore, reliability of the rectifying element and the AC generator using this rectifying element is improved by using this method. If the rectifying element is soldered to the radiating plate, the solder starts melting when the temperature of the rectifying element or the radiation plate exceeds the melting point of the solder. The rectifying element is press-fitted in the radiation plate in this method, and therefore the solder melting problem does not occur.
However, galling occurs in some materials in a pres-fitting process in which a base of the rectifying element is press-fitted in the hole formed in the radiation plate. If the base, which is an inserting member, and the radiation plate, which is a receiving member, are made of a copper material, the galling occurs.
When the inserting member is inserted in the hole of the receiving member, an excess is produced between surfaces of the inserting member and the receiving member due to the ductility and the tenacity of copper. The excess is pushed in the inserting direction of the inserting member and hardened as the press-fitting process proceeds because space for releasing the excess is not provided.
When the hardness of the excess becomes higher than the hardness of the inserting member, the inserting member is cracked and its outer periphery partially looses contact with the inner periphery of the receiving member. Namely, a contact area between the outer periphery of the inserting member and the inner periphery of the receiving member decreases. As a result, the tightness of physical and electrical connection between the inserting member and the receiving member decreases. Furthermore, large stress applied to the inserting member due to the hardened excess affects the productivity in the press-fitting process.